Gas chromatography (GC) is widely used for analysis of volatile organic compounds (VOCs) and other analyte compounds. GC systems also typically include an analyte detector when used for analysis. Flame ionization detectors (FIDs) are commonly used vapor detectors for bench-top GC instruments. FIDs have a high sensitivity (detection limits on the pico-gram scale), large dynamic range (6 orders of magnitude), and zero dead volume. Miniaturized FIDs (μFIDs) are being developed for portable applications. However, FIDs and μFIDs are destructive and cannot be placed in the middle of vapor flow path to monitor multi-dimensional GC separation. Instead, they are used only in the terminal end of a GC instrument. Furthermore, the required use of hydrogen hinders their broad acceptance in μGC devices.
Thermal conductivity detectors (TCDs) and μTCDs have also been used as a vapor detector. They are non-destructive and have a flow-through design. However, TCDs suffer from low sensitivity (nano-gram) and require helium. Electron capture detectors (ECDs) are another type of non-destructive vapor detector. While they are very sensitive, they have a limited dynamic range and need to use radioactive materials for analyte ionization. Recently, many other types of miniaturized non-destructive vapor detectors have been developed for μGC applications, including surface acoustic wave (SAW), chemi-capacitors, chemi-resistors, optical vapor sensors, and nano-electronic sensors. These sensors are small in footprint and non-destructive. However, they may suffer from large dead volumes, low sensitivity, electrical-optical-electrical conversions (for all optical vapors sensors), or limited vapor types. In addition, those vapor sensors usually require polymer coatings on their surface to capture and interact with analytes, which may limit the types of analytes detected and/or slow down the detection speed due to the absorption and desorption processes.
A photoionization detector (PID) is another type of vapor detector that has been under development for the past 50 years. They are sensitive (pico-gram), non-destructive, and applicable to a wide range of vapors. PIDs are non-destructive and can be used to detect a variety of organic and inorganic compounds. Furthermore, they have a large dynamic range (six orders of magnitude). Nevertheless, PIDs suffer from tardy response times resulting from the large ionization chamber and dead volume, so the use and integration of the PID in GC systems has been limited. It would be desirable to have a rapid PID detector with improved response times and high analyte sensitivity.